Here is what do, take a step back and observe the exterior from a acouple of steps away, thus way you can easily identify body panels that has been worked on, the paint will clearly show the differences. Now move closer and inspect the exterior all round, panel gaps, lights, scratches and everything.
Then the interior, check if everything is nice and clean, check if everything is working, aircon, wipers etc. If the car is clean chances are thst it was well cared for, you will even notice if it was cleaned for that specific purpose of selling, it won't be perfect, dust inside the vents etc.
Now the engine, the first thing you will notice will be oil leaks if there are any, the engine could have been washed so you will need to take your time here. Look for loose and untidy wiring that does look original, look around the radiator, hoses for coolant leak, check the coolant bottle for cracks and if there is enough coolant. Check the dipstick and see if the oil is clean, all the while note everything that is not in a good condition down, that is what you will bargain with.
Start the car and let it idle, observe any unusual noises, pulleys belts etc, the salesman will obviously want to rush you through the process, ignore them and take your time, rev the car and listen some more. Check for the smooth operation of the gear and clutch while the car is still cold.
Now turn the wheel and inspect the CV joints, brakes and shocks. Test drive the car and observe any issues. Now thank the salesperson for his time and go sleep on it. I used the transunion app before to do the verification on the car, it checks stolen status, accidents, insurance claims and all that. Bring a friend tomorrow and let them look at the car test drive some more. If you are happy as for the car papers have a look at them and compare to the disc, check the engine number on the block and compare, check the spare wheel, extra keys, Jack, wheel spanner and mag lock nut thing if any.